Myelin. Fatty substance (phospholipids, cholesterol, etc.) with protein, making a sheath to larger nerve fibers of vertebrates; formed by lamellar extensions of Schwann or glial cells tightly wrapped spirally around each nerve fibre.

Myelitis. Inflammation of the Mylenin Sheath surrounding the spinal cord.

Myeloid Tissue. Tissue producing myeloid elements (polymorphs and red blood cells) of vertebrate blood, which are formed throught life.

Myoplasma. The cytoplastic sol content of a muscle cell.

Myosin. Protein that in conjunction with actin provides the contractile mechanism in other cells. Myosin molecules are usually associated in filaments. A myosin molecule has an attachment site for actin, and an enzymic site that breaks down ATP with liberation of energy for contraction. The generally accepted sliding filament hypothesis ascribes contraction to myosin molecules sliding along actin filaments.

Myxamoeba. A naked, non-flagellate amoeboid cell, produced on the germination of a spore of the Myxothallophyta.

Myxobacteria. Small group of rod-shaped bacteria that are distinguished by gliding movement in contact with solid surface and by delicate, flexible cell wall. In many myxobacteria vegetative cells mass together to form minute ‘fruiting bodies’.

Myxovirus. One of a group of RNA-containing viruses associated with various diseases of man and other vertebrates. Orthomyxoviruses produce. diseases of the respiratory tract, e.g. influenza; paramyxoviruses include the causal agents of measles, mumps, and fowl pest.

Myeloma. A cancerous tumour of the bone narrow.

Myoblast. A cell that gives rise to a muscle fibre

Muscarine. A poisonous alkaloid occurring in certain mushrooms.